In this study we will take advantage of the ease of manipulation of yeast for the study of the regulation of mitochondrial biogenesis as influenced by the determinants of lipid synthesis, especially phospholipid synthesis. (a) Attempts are being made to isolate lipid mutants, including temperature sensitive mutants for the CTP phosphatidic acid cytidyl transferase to further elucidate the role of lipids in the control of mitochondrial biogenesis. (b) We will continue to probe the mechanism that determines the differential synthesis and assembly of cytochrome oxidase in unsaturated fatty acid auxotrophs of yeast grown in cis or trans fatty acids.